Print PageMany spring ephemerals can reproduce both sexually and clonally. Pollination and seed production can be stochastic due to highly changeable weather in early spring. Clonal reproduction can provide temporary reproductive assurance during years when pollination fails, but extensive clonal growth may indirectly interfere with pollination by altering the spatial distribution of genotypes. We studied the relative importance of clonal and sexual reproduction in populations of Dicentra canadensis, a self-incompatible clonal herb found in old growth deciduous forests in eastern North America. Demographic censuses were conducted for three years at three sites: one non-fragmented forest and two forest fragments surrounded by agriculture and suburban developments respectively. We constructed life history matrix models and performed elasticity analyses to quantify the relative contribution of sexual and clonal reproductive pathways to population growth rates. We also conducted supplemental pollination experiments during the census years to detect pollen limitation and estimate population growth potentials if seed set was not limited by inadequate pollinator services.
Results/Conclusions
Seed production varied significantly among sites. Plants in the non-fragmented forest produced on average 2.8 – 8.3 times more seeds than in the two fragmented sites for all census years. Supplemental pollination resulted in significantly more seeds per plant than natural pollination alone in some years but not all, suggesting strong yearly variation in pollinator services. Costs of flowering were manifested as reduced tuber production and increased likelihood of regression to a less productive stage year following flowering. However, seed production did not negatively affect tuber production or plant size in the subsequent year, hence the trade-off between seed and asexual reproduction was minimal. Population growth rates were near λ = 1 for all sites, with the highest seed set associated with the lowest λ-value. Elasticity analyses showed that survival of non-flowering plants capable of clonal reproduction was the most important life history transition for population growth; recruitment of seedlings contributed little, with elasticity values < 0.01 in all cases, even when seed set was maximized with supplemental pollination. Clonal reproduction appears to be crucial for the persistence of D. canadensis populations in environments with fluctuating pollination services. However, the long-term effects on genetic structure may reduce the population’s ability to reproduce sexually and therefore its ability to cope with environmental changes.
